1. Field of the Invention
The present invention relates to a thin-film dielectric and a thin-film capacitor element. In particular, the present invention relates to a thin-film dielectric capable of realizing a high dielectric constant and a thin-film capacitor element using the thin-film dielectric.
2. Description of the Related Art
Increases in density and integration of electronic circuits have been recently advanced with miniaturization and performance improvement of electronic apparatuses, and there have been demands for further miniaturization and thinning of capacitor elements serving as circuit elements which play important functions in various electronic circuits.
On the other hand, clock rising time is shortened with increases in operating frequency of integrated circuits. Further, power supply voltages are further decreased for aiming at lower power consumption of apparatuses. Under these conditions, a rapid change in load of an integrated circuit easily makes the drive voltage of the integrated circuit unstable. In order to normally operate an integrated circuit, it is necessary to stabilize the drive voltage.
For this purpose, a method for stabilizing a drive voltage is used, in which a decoupling capacitor is disposed between a voltage power supply line and a ground line of an integrated circuit. In order to realize the effective function of the decoupling capacitor, it is necessary to decrease an equivalent series inductance between the integrated circuit and the decoupling capacitor and to increase the capacity of the decoupling capacitor.
In order to decrease the equivalent series inductance between the integrated circuit and the decoupling capacitor, it is effective to arrange the decoupling capacitor as near the integrated circuit as possible and attempt to decrease the inductance of wiring between the integrated circuit and the decoupling capacitor.
For this purpose, a semiconductor device is disclosed, in which an interposer is disposed between a mounting substrate and a semiconductor chip mounted on the mounting substrate, a through via electrode (through hole electrode) is provided in the interposer, and a decoupling capacitor is formed on the surface of the electrode (for example, refer to Japanese Unexamined Patent Application Publication No. 2001-326305). In the semiconductor device, silicon or glass is used as an insulator for the interposer, and a thin-film capacitor element is formed on a silicon or glass substrate by using a thin-film technique.
From the viewpoint of the degree of design freedom, a thin-film capacitor element using a thin-film dielectric has been widely used as a decoupling capacitor which satisfies the requirement described above for an integrated circuit and the like. Materials such as SiO2, Si3N4, and the like have been used as materials for thin-film capacitor elements, but high dielectric constants cannot be obtained by these materials. Examples of materials having relatively high dielectric constants include perovskite-type oxides such as (BaSr)TiO3, BaTiO3, SrTiO3, and the like. A thin-film capacitor element with high capacitance can be achieved by using a material having a high dielectric constant and by thinning a dielectric layer. However, leak currents are degraded by thinning the dielectric layer.
In order to improve leak currents by using a material with a high dielectric constant, there is proposed a thin-film capacitor element including a thin-film dielectric layer which stores charge, and a pair of electrodes formed to face each other with the thin-film dielectric layer provided therebetween. The electric layer has a perovskite structure represented by general formula ABO3 (A is at least one of strontium (Sr), barium (Ba), and calcium (Ca), and B is at least one of titanium (Ti) and zirconium (Zr)), and contains 0.05 atomic % or more and less than 0.30 atomic % of at least one of vanadium (V), niobium (Nb), tantalum (Ta), antimony (Sb), bismuth (Bi), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), gadolinium (Ga), and holmium (Ho) (refer to, for example, Japanese Unexamined Patent Application Publication No. 2001-220300). In this literature, SrTiO3 containing 0.10 atomic % of Nb, BaTiO3 containing 0.30 atomic % of La, SrTiO3 containing 0.05 atomic % of V, and the like are described as examples of a material for the dielectric layer, and a leak current of about 10−8 A/cm2 is obtained.
However, in order to further decrease the size of an apparatus, a dielectric thin film having a high dielectric constant is required. According to Japanese Unexamined Patent Application Publication No. 2001-220300, a high dielectric constant is realized by forming a superlattice structure in which a BaTiO3 epitaxial film and a SrTiO3 epitaxial film are alternately stacked.
In addition, although a high dielectric constant is achieved by the superlattice-structure thin-film dielectric described in Japanese Unexamined Patent Application Publication No. 2001-220300, a special single crystal substrate is required for epitaxial growth, thereby causing difficulty in industrial use.